These are Electro-Harmonix EL84EH power tubes in platinum matched sets. The EL84 is the most common low power pentode tube popularized in early Vox AC30 amps. Rediscovered by Matchless amps and now currently used by nearly every tube amp company. Delivers quick soft overdrive distortion great for recording but usually too low volume for live gigs. Electro-Harmonix's platinum matching process consists of a 24-hour tube burn-in period followed by a bias plate current measurement in milliamps. Soft medium and hard style descriptions refer to break up modes of the tube for an overdriven guitar signal. Soft-rated tubes break up easier and have the least headroom yielding a heavier harder distortion. In comparison hard-rated tubes break up harder and have the most headroom yielding a cleaner clearer distortion while medium-rated tubes fall in between.